A process for the cryogenic distillation of an air feed to produce a low to medium purity oxygen product using a single distillation column system is taught in the art. Specifically. U.S. Pat. No. 4,382,366 by Gaumer and U.S. Pat. No. 4,707,994 by Shenoy et al. teach such a process.
A key feature in both Gaumer and Shenoy are the methods used to provide (1) reboil to the bottom of the distillation column and (2) reflux to the top of the distillation column. In both Gaumer and Shenoy, reboil is provided by heat exchanging pressurized air feed against the liquid phase at the bottom of the distillation column in order to at least partially condense the air feed and at least partially reboil the liquid phase. In Gaumer, the resulting condensed feed air is used directly as reflux. In Shenoy, the resulting condensed feed air is indirectly used to provide reflux by first reducing its pressure across a valve and subsequently heat exchanging it against the vapor phase at the top of the distillation column in order to partially condense the vapor phase. The condensed vapor phase is then used as reflux.
There is a concern with Gaumer and Shenoy, however, in that the above reflux methods may not be the most efficient way of providing reflux to the single distillation column system. It is an object of the present invention to more efficiently provide reflux to the single distillation column system and thereby more efficiently produce the low to medium purity oxygen product.